1. Field of the Invention
The present invention relates to valves and, more particularly, pertains to high pressure valves.
2. Description of the Prior Art
Conventional high pressure rotary valves, such as plug and ball valves, generally comprise a valve body defining a fluid passage in which a rotary closure member having a bore extending therethrough is mounted to selectively block or allow the flow of a fluid. A stem is provided to rotate the closure member between an open position in which the bore through the closure member is in alignment with the fluid passage of the valve body and a closed position in which the bore through the closure member extends transversely to the fluid passage of the valve body. The stem extends from the interior of the valve body through a stem passage normal to the fluid passage. Typically, a bonnet is bolted to the valve body for cooperating with a shoulder provided at the bottom of the stem to prevent the same from being blown out when submitted to high internal fluid pressure. Alternatively, the stem may be inserted through one end of a single piece valve body and then internally retained in place by means of an internal abutment surface defined in the stem passage of the valve body for cooperating with the shoulder provided at the bottom of the stem.
Although the above stem and valve body connections are efficient to prevent the stem from being blown out of the valve body, they substantially increase the torque required to operate the valve. Accordingly, a washer is generally installed between the stem shoulder and the cooperating abutment surface of the valve body in order to reduce the operating torque. However, in applications where the processed fluid is at a relatively high temperature, the installation of such a washer is problematic.